1. Field of the Invention
The present invention relates to an optical beam scanner used for reading a bar-code from omnidirectional light beam patterns in a POS (Point Of Sales) system.
2. Description of the Related Art
The POS system is now widely used in supermarkets and department stores for the sales management of goods and to speed up the checkout operation.
This system comprises a beam scanner for scanning a bar-code printed or attached to goods by a scanning light beam and converting the detected optical information into data suitable for computer-processing, a computer for processing the obtained data, and a POS register for connecting the beam scanner to the computer and displaying the necessary information to a customer.
In this regard, as illustrated in FIG. 9 a "bar-code" is a combination of thin and thick black lines 50, 51 and wide and narrow spaces 52, 53: these being variously arranged to represent a specific character, numeral, or symbol.
The bar-code is scanned by a beam scanner, such as a wand, a laser scanner, or a CCD scanner, which detects the variation of intensity of a light scattered by the bar-code on which the beam is incident; and converts the same to an electric signal.
Among known beam scanners, the laser scanner, which comprises a means for displacing a laser beam across a bar-code printed or attached to goods and moved laterally over a window of the scanner housing by an operator, a means for detecting a beam reflected from the bar-code, including various intensity variations corresponding to black and white areas on the bar-code, and a means for converting an optical signal obtained from the detected light intensity into an electric signal and decoding same as bar-code information, is most widely used.
To raise the efficiency of the checkout operation, an easily operable optical beam scanner must be used. Particularly, the bar-code must be accurately read even though a label carrying the bar-code is variously disposed on the goods, so that it is not necessary for the operator to orient the bar-code label in only one direction during the scanning. This function is known as "omni-directional readability".
To maintain the "omni-directional readability" at a high level even when reading a bar-code based on truncated symbols having bars approximately half the length of standard bars, the laser beam must be scanned along omni-directional scanning patterns; for example, in a horizontal scanning line for reading bar-code symbols oriented approximately in the horizontal direction, in a vertical scanning line for reading symbols oriented approximately in the vertical direction, and in an oblique scanning line for reading symbols oriented approximately in a direction between the horizontal and the vertical.
Further the beam scanner must be compact, to ensure a wider field of application to various checkout systems currently used in the merchandising industry.
To obtain such omni-directional scanning patterns, a beam scanner provided with a rotary mirror is used, as illustrated in FIG. 7. In this scanner, a laser beam 2 projected from a laser tube 1 is deflected by small mirrors 5, 6 and a large mirror 9, and received by a rotary mirror 29 through a flat area 81 of a combination lens 8. In the drawing, reference numeral 10 designates a scanner housing.
The body of the rotary mirror 29 has a conical shape, and two flat reflection surfaces 29a are arranged on the opposite slants of the cone, symmetrical with each other relative to a central axis of the cone, so that the reflection surfaces 29a are directed downward. The beam incident on the reflection surface 29a is deflected to a first mirror 15 disposed therebelow, and reflected thereby to a second mirror 18 associated with the first mirror 15. Note, usually a plurality of pairs of first and second mirrors are provided, but only one pair is illustrated in FIG. 7, to clarify the drawing. The beam reflected by the second mirror 18 emerges from the scanner through a window 21, in an obliquely upward oriented direction. This beam traces, for example, a horizontal scanning pattern e (see FIG. 8) on the window surface.
As the rotary mirror 29 is driven to rotate about its axis by a not shown motor, the beam deflected by the reflection surface 29a is received by another pair of first and second mirrors, and traces another scanning pattern other than the horizontal pattern, and accordingly, omni-directional scanning patterns a through e can be obtained on the window surface. If more scanning patterns are required, the number of pairs of first and second mirrors can be increased accordingly. In FIG. 8, reference numeral 22 designates an imaginary vertical plane.
As shown in FIG. 7, a bar-code carried on a label attached to goods 24 is moved across the window 21 and illuminated by the laser beam tracing one of these omni-directional scanning patterns. Part of the laser beam scattered by the bar-code corresponding to black and white areas thereof is returned to the scanner through the window 21 and reflected reversely along the above-described path. The returned beam is converged by the combination lens 8 and reflected by the large mirror 9 into a detector 28, which detects the pattern of the intensity variation containing the bar-code information. The intensity variation is converted to electric signals by the detector 28 and decoded as bar-code signals through a not shown A/D converter and decoder.
As stated above, the prior art fixed type laser scanner must be provided with a plurality of pairs of mirrors for selectively deflecting a laser beam reflected by a rotary mirror onto a plurality of flat mirrors arranged around a rotary axis thereof. This type of beam scanner, however, is very expensive due to the need for a plurality of mirrors, each of which must be manufactured and adjusted with a high degree of skill and accuracy. In addition, the intensity of the laser beam is dampened to a great extent due to the repeated reflections by the mirrors, which lowers the readability of the beam scanner. Conversely, if a high grade mirror having a better reflective efficiency is used to minimize this dampening of the beam intensity, the manufacturing cost of the beam scanner is further increased. Note, such a beam scanner is disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-194586 and U.S. Pat. No. 4,799,164.